Integrated circuits are becoming increasingly powerful and complex. Greater complexity implies greater circuit density and faster circuit operation which, in general, increases the problems of heat generation due to the operation of the integrated circuit (IC). If heat is not properly dissipated from an integrated circuit, it may, over time, malfunction or fail.
One of the most common and effective methods of dissipating heat generated by an integrated circuit is by use of a "heat sink", which includes a thermally conductive material which conducts heat away from the integrated circuit and then dissipates the heat into the ambient environment. The heat sink is placed in thermal contact with either the package of an integrated circuit (for packaged integrated circuits) or with the integrated circuit die itself (for unpackaged integrated circuits) to moderate the temperature of the IC.
There are two major categories of heat sinks. A first category includes heat sinks that attach directly to an integrated circuit, either with clips, other fasteners, or by means of an appropriate adhesive. This type of heat sink tends to be somewhat unreliable since it can become dislodged from the integrated circuits by, for example, an inadvertent lateral force exerted on the heat sink or due to thermal cycling of the IC. Also, these types of heat sinks do not protect packageless ICs from lateral forces, i.e. forces in an x-y plane parallel to the IC. This is a problem because packageless ICs are quite fragile, and their interconnections to a printed circuit board, interposer, or the like are easily damaged by lateral forces.
A second category of heat sinks includes heat sinks that are attached directly to the printed circuit PC boards which support the ICs. These types of heat sinks tend to be more reliable than the first category of heat sinks because they can be firmly attached to the PC board and because they better protect the ICs that they are cooling. However, they tend to be more expensive to manufacture and install than the first category of heat sinks. They also have the problem of applying a correct amount of force to the upper surface of an integrated circuit to ensure good thermal conduction but without damage to the IC.
This problem of applying the correct amount of force to an IC with this second category of heat sinks is particularly important to address with the "packageless" integrated circuits being increasingly used in industry. While packageless ICs tend to be of high performance and lower cost than traditional packaged ICs, they are more fragile due to their lack of a protective housing. Examples of technologies which utilize packageless integrated circuits include Tape Automated Bonding (TAB), Direct Chip Attach (DCA), and some Ball Grid Array (BGA) technologies.
The prior art has addressed this problem in two basic ways. One solution is to make a heat sink with resilient spring members which ensure that a proper amount of pressure is applied to the IC by the heat sink. These heat sinks, however, have multiple parts (including a number of small leaf springs) which add to the cost and reduce the reliability of the heat sinks. Another solution is to produce unitary heat sinks with "standoffs" which ensure that the proper amount of pressure is applied to the IC by the heat sink after the heat sink is attached to the PC board.
Prior art unitary heat sink designs are typically manufactured by first rough-forming a heat sink body (such as by molding, extrusion, etc.) and then by machining (such as with a rotary mill) the heat sink body to form the appropriate standoffs. A standoff is a mass of material which ensures that the portion of the heat sink that is in contact with the integrated circuit is at about the right distance from the printed circuit board supporting the integrated circuit, i.e. it is has a height that is about the same as the distance from the top of the integrated circuit package to the surface of the printed circuit board. Due to the large number of manufacturing steps, these unitary heat sinks of the prior art tend to be quite expensive.
Furthermore, the distance from the top of the chip package to the circuit board tends to vary from IC to IC due to differences in die or package sizes, the amount of glue or solder used to attach the die to the printed circuit board, and other factors. Therefore, unitary heat sinks of the prior art that rely on standoffs must be manufactured for each different integrated circuit size and mounting technology. This reduces economies of scale in the production of the heat sinks, and increases inventory costs.